What are "Flow Limited Cycles"?

[Brian000]

I'm using a PB 420E and SL software.

My "Flow Limitations - Runs" are 1789 for the past 96 hours, an index of 18.7/hr. Under "Cycle states" I have a Flow Limited Cycle of 13%, Normal Cycle 85%, and Intermediate Cycle 2%.

What do these numbers mean and are my numbers normal or concerning?

Thanks in advance.

Brian.

[Snoredog]

Motorcycles with mufflers????

My guess:
Cycles is PB's way of determining the amount of resistive breathing you have experienced during the session if that makes sense (cycles are like number of breaths you have taken). Let's say you start off with 100% of Normal breathing for the session, subtract from that all the Flow limited breaths or periods (includes FL's, HI and Apnea) and the pie chart shows you out of the session Normal breathing, Flow Limited breathing and Other. As for other that must be the cumulative total of all the events combined. This (I think) is associated with Flow Limited Runs which are events not severe enough to be classified by the machine as a Hypopnea or other more severe event.

The Silverling manual does not spell this out (that I could find) so the above is just my guess. When you have fewer events the number of Normal cycles increase (mine avg. around 95%) and Flow Limited Runs decrease.

If my guess doesn't make sense then use the first guess at the top

FYI: You can go into your SL3 directory and copy the 420e manual in PDF format to another location to view it. These PDF files make up the help files so you need to leave the originals in the directory, but if you copy them to another location you can view them like any other PDF file. It won't allow you to cut-n-paste any content unless you can print the PDF to another PDF file. On a Mac you select PDF as one of your print options.

Sorry, I've tried to find a better description of Cycles and FL Runs and there isn't a lot of information about it, that is why it is only a guess, like most things on those reports the fewer you have the better except for amount of sleep you get.

[tangents]

While I don't have a good understanding of the algorithm for flow limited cycles, I do know that when the machine senses a flow limitation, it will bump up your pressure until it either goes away or the upper limit is reached. When you have a high index like you do, my gut feel is that you're not getting restful sleep. When I have had data like that, I have raised my lower limit a little (I actually have my lower limit at my titration value) and the normal cycles are now at 98%.

Hope that helps a little,
Cathy

[echo]

For a great looooooong technical read on Flow limitations, and the 420e ability to handle them, check out
Topics: UARS obstructions, 420e, etc.

I believe the % of flow limited cycles is based on the amount of time spent in a flow limited breathing state. The 420E manual states that each cycle is one measurement of the air flow, (but I dont know the amount of time between each measurement) so at any one measurement in your breathing you may be breathing in a normal, intermediate, limited, etc, way.

Edit: Not sure if it's something to be concerned about or not. Maybe people report that they have high flow limitation numbers and they still feel OK. Some people have 'shallow breathing' that's actually normal for them, but it's flagged as a flow limitation (and thus the discussion to turn of the IFL1 setting). That was not the case for me. After slightly increasing the pressure, I've gone from a Flow limited cycle of 5-15% to now less than 2% and I feel tons better (in straight CPAP mode).

[Brian000]

Thanks, Echo. That is useful.

What I'm struggling with is that my AHI is about 1 (which is really good!!), but my Flow Limitation Index is soooo high -- about 18. And no, I'm still not getting great sleep. I'm wondering if the high flow limitation might be a clue to something. Maybe I should just share this data with my sleep doc.

I have turned off IFL1 and now at least the machine doesn't rev way up and run at my highest setting.

[echo]

Brian - here's the longer version of my flow limitations adventure: Five months in and not getting anywhere
My confusion with UARS was that it seemed to be that you would have either UARS or OSA... but even with the OSA treated (my PSG said 35 AHI and 39 RDI) I was still getting the flow limitations. Maybe I don't have UARS, but with the flow limitations down I am feeling sooo much better. And I noticed the positive change just after a few days on the new pressure on straight CPAP.
When I was running in APAP mode I had also turned off IFL1 thinking that the flow limitations were normal - because I didn't sleep well at ALL on APAP mode (but maybe the settings were wrong) - and I think that's because the pressure was jumping from 7 or 8 to 10 for the flow limitations, and the jump was many too much for me so it kept waking me up. I might try APAP on a range closer to 10 now.

As I mentioned, many people have the flow limitations without problems, but it might be worth addressing. I've been at this for a year and I just think how much suffering I could have avoided if I had *just* tried the 10.5 months earlier. But I was worried about centrals showing up (which was reported at my titration at 10 or above), so I never went above 10. The sleep doc's only advice was use straight CPAP somewhere between 7 and 10 and to make changes based on how I felt.

But since you have the software, you can easily see what is going on at each pressure. I would indeed share that data with my sleep doc and see what they say.

Some other troubleshooting questions:
- Do you sleep mostly on your back?
- How long have you been on xPAP? (Your profile shows you joined in 2005).
- What were you titrated at and how is the 420E configured now? (Also note that Minimum and Initial pressures should be different).
- Were you sleeping well before and aren't now, or has your sleep been poor this whole time?
- Have you lost or gained weight?
- Do you have any other medical conditions? Have you been checked for other things, e.g. thyroid, diabetes, etc...?

If you want to titrate yourself using straight CPAP (to find the pressure which eliminates most of the flow limitations), read my post above to see how I did it. I found that way was easier and more controlled than using APAP mode.

Edit: OK I found the answers to my questions in viewtopic.php?f=1&t=32004&p=273194

What I would do if I were you --- (I'm not a doc, just from personal experience)
- Stop APAP mode and go to straight CPAP mode - avoid the ambiguity of nightly arousals due to the APAP changing pressure.
- Start at a pressure of 11.
- Stay at that pressure for a week. Check your AHI, flow lim runs, and number of central's and get an average and max for the week. (Did they notice central's on your titration or PSG?)
- Start exporting your SL data to Excel and make some averages. I can send you an example and instructions on how to do it easily, PM me if you need help.
- If your central's are low or 0, but flow lim's are high, increase by 0.5 every week until the flow lim's are a few %, and watch out for Central's. They can be just as distruptive to your sleep , or even more so, than flow limitations. Find the balance between reduced flow lim's and reduced central's.
- Share this data with your doc

Important: do you normally sleep on your back, and were you titrated on your back?? Some of our members here have found that they have outrageous numbers when on their backs (e.g. need 20cm), but when on their side their pressure needs are much lower.